The invention relates to a device for attaching a semiconductor chip to a chip carrier, thereby producing an electrically conducting connection between contact areas arranged on a surface of the semiconductor chip and contact areas on the chip carrier by means of an anisotropically conducting film or an anisotropically conducting paste.
In the production of electronic parts, use is more and more frequently made of a new process for producing the electrical connection between a semiconductor chip and the contact areas on a carrier, connected by conductor tracks, whereby the contact areas of the semiconductor chip are brought into direct contact with the contact areas of the carrier. The previously used package, housing the semiconductor chip, and which was provided with its own contact areas used for contact bonding, is hereby dispensed with. To produce the electrical connection between the contact areas of the semiconductor chip and the contact areas on the carrier, use is thereby made of an anisotropically conducting film or an anisotropically conducting paste, that is a material which offers a very low electric resistance in only one direction, whilst it is practically non-conducting in the direction perpendicular to it.
A problem when using such a film or such a paste to produce the electrical connection between the contact areas of the semiconductor chip and the contact areas of the carrier is that very narrow tolerances must be adhered to as regards the tools which are used to press the semiconductor chip against the film or the paste and the carrier, since a reliable electrical connection between the different contact areas of the semiconductor chip and the corresponding contact areas on the carrier can only be achieved when, on the one hand, the pressure applied is evenly distributed and, on the other, the thickness of the film or the paste between the areas in contact with each other is made as uniform as possible. The uniformity of the layer thickness is of great importance for the following reason. The anisotropic conduction behaviour of the film or of the paste used is achieved in that in a material, such as epoxy resin, electrically conductive particles are embedded which are not in contact with each other. In the direction of the surface extension of the film or the paste, respectively, this material therefore offers a very high electric resistance, but it assumes a low-resistance state when as a result of applied pressure it becomes so thin between two contact areas that the particles embedded in the epoxy resin come into contact with both the contact areas at the semiconductor chip and also with the contact areas at the carrier. These particles then produce a conducting connection between the contact areas. If, however, the semiconductor chip is pressed against the carrier in even a slightly slanting position, because of excessive tolerances, a situation may arise where the conducting particles cannot produce a conducting connection between the contact surfaces because they are not in contact with each other, and that the film or paste material is squeezed out at some contact areas to an extent that no conducting particles remain available between the contact areas to be connected. The desired electrical connection between the contact areas is therefore not realised at these points, so that the unit to be produced has to be scrapped. Especially in the case of semiconductor chips having a plurality of contact areas which are to be connected to the corresponding contact areas of the carrier, this requirement for a uniform contact pressure constitutes a problem that is difficult to solve.
The invention rests of the requirement to produce an embodiment of the device of the type described in the foregoing that will allow the desired electrical connections between the contact areas on the semiconductor chip and the corresponding contact areas on the chip carrier to be realised in a highly reliable way, without the need for stringent demands on the tolerance of the parts involved.
This requirement is satisfied according to the invention in the device described above by a pressure die for the application of pressure to the chip with an adjustable pressing force against the chip carrier, a counter-pressure support for receiving the chip carrier with the semiconductor chip arranged on it with the interposition of the anisotropically conducting film or the anisotropically conducting paste, and an elastic body arranged either between the pressure die and the semiconductor chip or between the chip carrier and the counter-pressure support.
The elastic body used in the device according to the invention takes care of the compensation of tolerances and ensures that the semiconductor chip is pressed in precisely plane-parallel alignment against the chip carrier, so that between the contact areas on the semiconductor chip and the corresponding contact areas on the chip carrier equal distances are obtained, which are essential for the establishment of reliable electrical connections between these contact areas.
In an advantageous embodiment, the elastic body can be attached to the face of the pressure die, or else to the surface of the counter-pressure support which receives the chip carrier. The elastic body can advantageously also be an elastic strip extending between the face of the pressure die and the surface of the chip. To accelerate the solidification of the electrical connection produced, the counter-pressure support may be heated to enable the anisotropically conducting film used or the anisotropically conducting paste used to set hard in a shorter time. The elastic body may advantageously be made of heat-resistant silicone.